(1) Field of the Invention
This invention relates to an ellipsometer, and a method and system for multivariable measurement of sample variables. More specifically, the invention relates to an algorithm that enables multiple variables to be measured and calculated using an ellipsometer, and a method for changing the wavelength of the light source of an ellipsometer. Samples for which this invention is used are thin films formed on the surface of a semiconductor and so forth, and more particularly, samples such as multilayer films that require multivariable measurement.
(2) Description of the Related Art
When measuring a sample by ellipsometry, monochromatic light is radiated onto a sample at a fixed incident angle. In this case, however, since only two variables can be measured, it has been thought that only two optical constants of the sample are obtained by following calculations. In actual samples, however, there are many cases in which it is necessary to measure three or more optical constants as in the case of multilayer films. Consequently, attempts have been made to increase the number of variables that can be measured such as by measuring while changing the incident angle to several different angles, or by using a white light source and switching the wavelength of the light radiated onto the sample with a monochromator (spectroscopic ellipsometer).
However, in the case of methods which change the incident angle of the light, since the shape of the spot formed by the light beam on the surface of the sample changes as the incident angle is changed, measurement with different incident angles cannot be considered to constitute measurement of the same location on the sample. In addition, the penetration depth of the light inside the sample also changes when the incident angle is changed. Thus, gathering measurements at different incident angles and analyzing those measurements as a single piece of data is not correct.
Known examples of spectroscopic ellipsometer include U.S. Pat. No. 5,329,357 of Bernoux, et al. issued on Jul. 12, 1994, and U.S. Pat. No. 5,166,752 of Spanier, et al. issued on Nov. 24, 1992. In these methods in which a monochromatic light is formed with a monochromator from a white light source, when an adequate amount of light is attempted to be obtained, the FWHM (full width at half maximum) of the spectral light increases resulting in problems with purity with respect to the wavelength of the light. Conversely, when the purity of the light is attempted to be improved by narrowing the slit width of the grating, the amount of light decreases, which not only causes a decrease in the S/N ratio of the measurement, but also lowers the parallelism of the light rays within the beam due to diffraction.
Because of these reasons ordinary spectroscopic ellipsometer varies the wavelength of input light in considerable wide range.
The present invention attempts to allow the obtaining of multivariable data from a sample using a method free of the above-mentioned problems during measurement using an ellipsometer.